The present invention relates to instrumental chemical analysis. More particularly, the present invention relates to an automated instrumental apparatus and method for carrying out sequential injection liquid-liquid extraction. The principal advantages of this automated technology over the prior art are elimination of the need for dynamic phase separation; on-line pre-extraction chemical conditioning; a substantial reduction in solvent, reagent, and sample usage; and a similar substantial reduction in waste generation.
In general, the present invention in a first aspect provides an apparatus for sequential injection liquid-liquid extraction. The apparatus comprises (a) a bidirectional precision pump for controlling fluid flow; (b) a holding/mixing coil, for holding and mixing liquids, and carrying out liquid-liquid extraction; (c) a selection valve, for withdrawing, transferring, and injecting a plurality of fluids; (d) a separation cell, for separating an extract phase from a raffinate phase; (e) a detector, for detecting the quantity of a component which was extracted from a sample by an extraction solvent; and (f) a microprocessor, for controlling the selection valve and the bidirectional precision pump.
In a second aspect the invention provides a method for sequential injection liquid-liquid extraction. The method comprises (a) using a bidirectional precision pump under suction to transfer a sample through an inlet line to a holding/mixing coil, to purge the inlet line; (b) discharging the sample from the holding/mixing coil; (c) flushing the holding/mixing coil with a carrier solvent, to remove residual sample; (d) disposing a plurality of liquid zones in the holding/mixing coil, using a microprocessor to control the selection valve; (e) mixing the zones and providing efficient contact between an extraction solvent and the sample by passing the plurality of liquid zones through the holding/mixing coil; (f) reversing the flow through the holding/mixing coil, to provide further mixing of the zones and further liquid-liquid contact between the extraction solvent and the sample; (g) transferring the liquid zones from the holding/mixing coil to a separation cell; (h) holding the liquid zones in the separation cell, to separate an extract phase from a raffinate phase; (i) withdrawing the extract phase from the separation cell; (j) transferring the extract phase to a detector, for determining the quantity of a component extracted from the sample; and (k) determining the amount of the component extracted by measuring the response of the detector.